1. Field of the Invention
The present invention relates to a process for isolating methacrylic acid by extraction. More particularly, the present invention relates to a process for isolating methacrylic acid from an aqueous methacrylic acid solution obtained by the gas phase catalytic oxidation reaction of one or more of isobutylene, tert. butyl alcohol, methacrolein or isobutyladehyde by extraction in an extraction column.
2. Description of the Prior Art
Methacrylic acid obtained from one or more of isobutylene, tert. butyl alcohol, methacrolein or isobutylaldehyde by gas phase catalytic oxidation reaction is purified generally by absorbing the reaction product obtained by the gas phase oxidation reaction in water, distilling the liquid to remove low-boiling products such as acetone and methacrolein, separating methacrylic acid from water in the extraction step and separating methacrylic acid from the extraction solvent by distillation. However, if said extraction process is carried out continuously, polymers deposit in large amounts in the extraction column or at an interfacial surface part in the extraction step to make the operation in the extraction column impossible after a relatively short period of time. As a result, the inside of the column must be washed every 3-7 days which is disadvantageous. Further, the emulsion is apt to be formed in an upper part of the extraction column, which emulsion often causes flooding, resulting in suspension of the operation in the extraction column each time.
The emulsion thus formed is different from an emulsion formed, for example, when the rotation rate of a rotary extraction column is extremely high. The former emulsion comprises foam with bubble diameter of around 1 mm. It is formed even when rotation rate of the extraction column is low and produces a so-called emulsion phase in addition to the solvent phase and aqueous phase in the extraction column. Once the emulsion phase has been produced, the continuation of the operation in the extraction column becomes impossible unless the emulsion phase is taken out from the extraction column.
After intensive investigation to overcome those problems, it has been found that the emulsion formation is caused by high-boiling materials mainly comprising methacrylic acid polymer.
A need, therefore, continues to exist for a process for extracting methacrylic acid from an aqueous methacrylic acid solution which contains high boiling materials mainly comprising methacrylic acid polymer.